The present invention is directed generally to a laser, and more particularly to a diode laser-pumped, solid state microchip laser.
Single element, microchip lasers are known for producing single mode outputs when the free spectral range of the laser cavity is larger than the bandwidth of the gain transition in the active material. The interaction between two or more oscillating modes typically produces a noisy laser output, and so single mode operation is advantageous for applications requiring low noise signals.
However, the cavity length is increased when other elements, in addition to the gain medium, are added to the microchip laser cavity. This typically reduces the free spectral range of the cavity to a value less than the gain bandwidth of the active medium, and multi-mode operation results. Multi-mode operation is particularly a problem when it is desired to add a nonlinear component to the microchip laser cavity for generating a frequency other than the fundamental laser frequency.
Multi-mode operation is also a limitation where the gain bandwidth of the active medium is broad, as is usually the case with a tunable laser medium. In such a case, frequency selection elements have to be placed within the laser cavity to produce single longitudinal mode operation, thus complicating the design and manufacture of a tunable, single mode laser.
Therefore, there is a need to produce a microchip laser that can incorporate additional elements for frequency selection and nonlinear frequency generation while still maintaining single mode operation.